The present invention relates to the field of optical correlator and image clean up and devices. Correlators have been under extensive study for more than a decade, due to their significance in various applications of science and technology. They have been proposed for use in a variety of application such as security, finger print identification and machine vision (H. Rajbenbach, S. Bonn, P. Refregier, P. Joffre, J. P. Huignard, H. S. Jensen and E. Rasumussen, xe2x80x9cCompact photorefractive correlator for robotics applications,xe2x80x9d Appl. Opt. 31, 5666-5647 (1992) and tracking(Allen Pu, Robert Denkewalter and Demetri Psaltis xe2x80x9cReal-time vehicle navigation using holographic memory,xe2x80x9d Opt. Eng 10, 2737-2746, (1997). K. Curtis and D. Psaltis, xe2x80x9c3-dimensional disk based optical correlator,xe2x80x9d Opt. Eng. 33, 4051-4054 (1994).
So far, to my knowledge, three successful optical correlators have been built for this tracking purpose, The first is the TOPS one TOPS optical correlation programLindell, Scott D.; AA(Martin Marietta Astronautics Group) Publication: Proc. SPIE Vol. 1958, p. 7-18, Transition of Optical Processors into Systems 1993, David P. Casasent; Ed. The size of this correlator is less than a one cubic foot, and manages to correlate 800 correlation per/sec. For this correlation the binary phase-only filter was used in the correlation plane. This correlator proved its success in tracking. A more compact correlator was built by Cortec, Inc(11) at Burlington Mass. For this correlator quantum well photorefractive materials with response time of less than xcexcsec time were used. The size of this correlator was the size of a hand and managed to correlate nearly 10,000 correlations per sec. A group in Caltech demonstrated an opto-electronic correlator which can correlate 30,000 correlation per/sec(K. Curtis and D. Psaltis, xe2x80x9c3-dimensional disk based optical correlator,xe2x80x9d Opt. Eng. 33, 4051-4054 (1994) This correlation system has been successful in real-time vehicle navigation. This correlation system uses a holographic data base of correlation filter stored on a DuPont HRF-150 photo polymer.
In accordance of the present invention, a design of a compact optical correlator with operating speed exceeds 1,000,000 correlation/sec is illustrated. Correlator with this massive capability can be used in variety of application involved a large data base for comparing such as finger print identification, information search on the Internet, DNA sequence codes. Templates for machine vision.
A matched amplification correlator of FIG. 3a for correlating a noisy cluttered weak signal image with a strong reference image is provided in a first embodiment of the invention, wherein Fourier transforms of these images produce a real time hologram upon a photorefractive holographic storage device and a spatial light modulator, optically coupled to the storage device, modulates the hologram with a correlation filter, and the modulated signal is Fourier transformed to produce an output correlation signal.
In a second, presently most preferred embodiment of FIG. 3b, overlapping Fourier transforms of beams bearing the signals to be correlated are projected upon a controlled absorption modulator having beam control III-V family semiconductor layers for selectively switching the Fourier transform of the noisy cluttered image through the device, and a spatial light modulator, optically coupled to the storage device, modulates the hologram with a correlation filter, and the resulting modulated signal is Fourier transformed to produce an output correlation signal. This embodiment can operate at extremely high speeds. As explained in the FIG. 1 description, assuming that 100 images are fed simultaneously from image input multiplexer 103 of FIG. 1 through an image rotator 113 into the compact correlator 123, it should be possible to achieve nearly one hundred million correlations per second (0.1 Ghz) if correlator 123 has a FIG. 3b configuration. The image cleaning processors of FIGS. 2(b) and 2(d) are useful standing alone for cleaning noisy cluttered images, and are advantageously used as front end apparatus"" in connection with the inventive correlators of FIGS. 3(a) and 3(b) respectively.